Typically when edge emitting semiconductor laser devices or other edge input/output semiconductor optoelectronic devices are fabricated on a III-V semiconductor wafer, it is desirable to align input or output facets of the device perpendicular to or parallel with a wafer crystal cleavage plane. Often such alignment is not performed exactly, and typically there is an offset angle between a pattern of devices formed on the wafer and a cleavage plane adjacent the facets. This effect is termed “run-out”, and has an impact on the device yield from a wafer.
“Run-out” can be understood to be a distance accumulated by the cleavage crystal plane away from the pattern of devices fabricated on the wafer. It impacts on the yield of devices from a given wafer since the cleave will not be in the same place for all devices along the cleave. This is a significant problem as the device facets so formed will not match-up as intended to where the contact pattern on the device is formed. However, to ensure the intended operation of each device, the active regions thereof (ie where one of the contacts is located) must operate in the designed fashion.
Further, in devices having contact layers such as relatively thick gold plated plates, (eg 2 to 3 microns), cleaving the devices out of the wafer causes problems as the contact layers may tend to delaminate. It is known to provide devices having metallic, eg gold layers, which are used as contact pads, heatsinking means, stress relief means and device handling protection means.
Yet further, when facet coatings are provided, eg on laser diodes, typically some of the coating may overlap onto other surfaces of the device. This results in insulation of this overlapped part of the device from electrical contact. Thus, if so-called “junction side down” bonding is attempted in such cases, good electrical and thermal communication is not possible with the device via the overlapped part.
It is an object of the present invention to obviate or at least mitigate the aforementioned problems in the prior art.